Immersion cooling system that enables increased heat flux at heat-generating components of computing devices

ABSTRACT

An immersion cooling system includes an immersion tank that is configured to retain dielectric working fluid and to hold a plurality of computing devices submerged in the dielectric working fluid. The immersion cooling system also includes a condenser that is configured to cause condensation of vaporized working fluid. The immersion cooling system also includes a subcooling heat exchanger that is in fluid communication with a coolant source. The coolant source provides coolant having a coolant temperature that is lower than a boiling point of the dielectric working fluid. The subcooling heat exchanger is positioned so that heat transfer can occur between the dielectric working fluid and the subcooling heat exchanger. The immersion cooling system also includes a control system that controls how much of the coolant flows into the subcooling heat exchanger based at least in part on a temperature of the dielectric working fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. patentapplication Ser. No. 17/320,063, filed on May 13, 2021, which is herebyincorporated by reference in its entirety.

BACKGROUND

Computing devices include heat-generating components that producesignificant amounts of heat during normal operation. Examples of suchheat-generating components include central processing units (CPUs),graphics processing units (GPUs), tensor processing units (TPUs), memorydevices, and other integrated circuits.

Computer cooling is the process of removing heat generated byheat-generating components within a computing device to keep componentswithin permissible operating temperature limits. Cooling can beimportant because computer components are susceptible to temporarymalfunction or permanent failure if they are overheated.

A datacenter is a physical facility that is used to house computingdevices and associated components. A datacenter typically includes alarge number of computing devices (e.g., servers), which may be stackedin racks that are placed in rows. A colocation center is a type ofdatacenter where equipment, space, and network bandwidth are availablefor rental to customers.

A datacenter typically includes a cooling system to enable the computingdevices within the datacenter to continue working within their specifiedthermal limits. Many computing devices use air for cooling systemcomponents. This requires datacenters to utilize air-based coolingtechniques to transfer the heat to the external environment. Air has alow specific heat capacity, which means that large amounts of air arerequired to remove a watt of heat. Air-based cooling techniques oftenrequire expensive infrastructure components such as computer room airconditioning (CRAC) units, air conditioner compressors, air circulationfans, duct work, air handlers, dehumidifiers, and the like.

One of the challenges in managing a datacenter is achieving the rightbalance between space and power. For various reasons, power density hasincreased considerably over the last few years. As server racks becomemore thermally dense requiring greater quantities of air for cooling,the costs and logistics of conventional cooling using air becomesincreasingly challenging.

Some datacenters utilize immersion cooling techniques in which computingdevices are submerged in a thermally conductive, electrically isolatingdielectric fluid, which may be referred to as a dielectric working fluidor a heat transfer fluid. In an immersion cooling system, at least onecontainer (e.g., a tank) is filled with the dielectric working fluid,and computing devices are placed in the container. The container may bereferred to herein as an immersion tank. The dielectric working fluidhas a higher heat capacity than air. Thus, the dielectric working fluidrequires less fluid volume for a given heat load than air does.

Heat can be removed from the heat-generating components (e.g.,integrated circuits) within the computing devices by circulating thedielectric working fluid into direct contact with the heat-generatingcomponents, then through heat exchangers where the waste heat istransferred. Fluids suitable for immersion cooling have very goodinsulating properties to ensure that they can safely come into contactwith energized electronic components without significantly altering theelectrical characteristics of the system or system components. Immersioncooling has the potential to become a popular cooling solution fordatacenters because it allows operators to drastically reduce theirenergy usage through the elimination of the air cooling infrastructure.

Broadly speaking, there are two different types of immersion coolingtechniques: single-phase immersion cooling and two-phase immersioncooling.

With a single-phase immersion cooling system, the working fluid neverchanges state and always remains in a liquid form. In someimplementations, the working fluid may be actively circulated by pumpingthe dielectric coolant in, through, and around the computing devicesbeing cooled, and then transferring the heat absorbed by the coolant toa heat rejection device such as a radiator, dry cooler, liquid-to-liquidheat exchanger, or cooling tower. Alternatively, the working fluid maybe passively circulated by the natural convection of the heated coolantto the heat rejection device(s).

In a two-phase immersion cooling system, the heat of vaporization andthe specific heat capacity characteristics of the dielectric workingfluid are utilized for cooling. The dielectric working fluid generallyhas a relatively low boiling point such that heat absorbed by thedielectric working fluid surrounding the computing devices causes aportion of the dielectric working fluid to boil off or vaporize into agas. The phase change of the dielectric working fluid carries heat awayfrom the computing devices. The vapors produced by the boiling of thedielectric working fluid rise above the fluid pool where they contact acondenser that is cooler than the dielectric working fluid's boilingpoint. This causes the vapors to condense back into a liquid and fallback into the fluid pool.

SUMMARY

In accordance with one aspect of the present disclosure, an immersioncooling system includes an immersion tank that is configured to retaindielectric working fluid and to hold a plurality of computing devicessubmerged in the dielectric working fluid. The immersion cooling systemalso includes a condenser that is configured to cause condensation ofvaporized working fluid. The immersion cooling system also includes asubcooling heat exchanger that is in fluid communication with a coolantsource. The coolant source provides coolant having a coolant temperaturethat is lower than a boiling point of the dielectric working fluid. Thesubcooling heat exchanger is positioned so that heat transfer can occurbetween the dielectric working fluid and the subcooling heat exchanger.The immersion cooling system also includes a control system thatcontrols how much of the coolant flows into the subcooling heatexchanger based at least in part on a temperature of the dielectricworking fluid.

In some embodiments, the condenser can be located in a vapor space ofthe immersion tank, and the subcooling heat exchanger can be submergedin the dielectric working fluid.

In some embodiments, both the condenser and the subcooling heatexchanger can be embedded in an external wall of the immersion tank.

In some embodiments, the control system can include a temperature sensorthat measures the temperature of the dielectric working fluid, a valvethat controls a flow of the coolant to the subcooling heat exchanger,and a controller that controls opening and closing of the valve based atleast in part on the temperature of the dielectric working fluid.

In some embodiments, the controller can calculate an error value as adifference between a desired temperature of the dielectric working fluidand the temperature of the dielectric working fluid as measured by thetemperature sensor. The opening and the closing of the valve can bebased at least in part on the error value.

In some embodiments, the immersion cooling system additionally includesa pipe that is submerged in the dielectric working fluid. The pipe caninclude a plurality of nozzles and a pump that forces the dielectricworking fluid to flow through the pipe. The pipe can be positioned tocause a plurality of streams of the dielectric working fluid to exit outof the plurality of nozzles in a direction of at least oneheat-generating component on at least one computing device.

In some embodiments, the control system can be additionally configuredto proactively adjust coolant flow to the subcooling heat exchangerbased at least in part on an expected workload of the plurality ofcomputing devices.

In some embodiments, the immersion tank can additionally include adiaphragm that can affect a vapor space pressure in the vapor space ofthe immersion tank. Increasing the vapor space pressure can cause asaturation temperature of the dielectric working fluid to increase.Decreasing the vapor space pressure can cause the saturation temperatureof the dielectric working fluid to decrease.

In some embodiments, the diaphragm can be located in the vapor space ofthe immersion tank. The condenser and the subcooling heat exchanger canbe embedded in an external wall of the immersion tank.

In some embodiments, the immersion cooling system can additionallyinclude a relief valve connected to the diaphragm. The relief valve canbe configured to release pressure from the diaphragm when the vaporspace pressure equals the diaphragm pressure.

In accordance with another aspect of the present disclosure, animmersion cooling system includes an immersion tank that is configuredto retain dielectric working fluid and to hold a plurality of computingdevices submerged in the dielectric working fluid. The immersion tankincludes a vapor space above the dielectric working fluid. The immersioncooling system also includes a condenser that is configured to causecondensation of vaporized working fluid. The immersion cooling systemalso includes a subcooling heat exchanger that is in fluid communicationwith a coolant source. The coolant source provides coolant having acoolant temperature that is lower than a boiling point of the dielectricworking fluid. The subcooling heat exchanger is positioned so that heattransfer can occur between the dielectric working fluid and thesubcooling heat exchanger. The immersion cooling system also includes adiaphragm that changes a vapor space pressure in the vapor space of theimmersion tank. Changing the vapor space pressure also changes asaturation temperature of the dielectric working fluid.

In some embodiments, the diaphragm can be located in the vapor space ofthe immersion tank, and the condenser and the subcooling heat exchangercan be embedded in an external wall of the immersion tank.

In some embodiments, the immersion cooling system can additionallyinclude a relief valve connected to the diaphragm. The relief valve canbe configured to release pressure from the diaphragm when the vaporspace pressure equals the diaphragm pressure.

In some embodiments, the condenser can be located in the vapor space ofthe immersion tank, and the subcooling heat exchanger can be submergedin the dielectric working fluid.

In some embodiments, the immersion cooling system can additionallyinclude a control system that controls how much of the coolant flowsinto the subcooling heat exchanger based at least in part on atemperature of the dielectric working fluid.

In some embodiments, the control system can include a temperature sensorthat measures the temperature of the dielectric working fluid, a valvethat controls a flow of the coolant to the subcooling heat exchanger,and a controller that controls opening and closing of the valve based atleast in part on the temperature of the dielectric working fluid.

In some embodiments, the controller can calculate an error value as adifference between a desired temperature of the dielectric working fluidand the temperature of the dielectric working fluid as measured by thetemperature sensor. The opening and the closing of the valve can bebased at least in part on the error value.

In some embodiments, the immersion cooling system can additionallyinclude a pipe that is submerged in the dielectric working fluid. Thepipe can include a plurality of nozzles and a pump that forces thedielectric working fluid to flow through the pipe. The pipe can bepositioned to cause a plurality of streams of the dielectric workingfluid to exit out of the plurality of nozzles in a direction of at leastone heat-generating component on at least one computing device.

Another aspect of the present disclosure is directed to a method forsubcooling dielectric working fluid in an immersion cooling system thatincludes a plurality of computing devices submerged in the dielectricworking fluid. The method can include determining a desired temperatureof the dielectric working fluid. The desired temperature of thedielectric working fluid can be less than a boiling point of thedielectric working fluid. The method can also include calculating anerror value as a difference between the desired temperature of thedielectric working fluid and a measured temperature of the dielectricworking fluid. The method can also include causing coolant to flow to asubcooling heat exchanger based at least in part on the error value whenthe measured temperature of the dielectric working fluid is greater thanthe desired temperature of the dielectric working fluid. The method canalso include preventing the coolant from flowing to the subcooling heatexchanger when the measured temperature of the dielectric working fluidis less than or equal to the desired temperature of the dielectricworking fluid.

In some embodiments, the immersion cooling system can additionallyinclude a diaphragm having a diaphragm pressure and a relief valveconnected to the diaphragm. The method can additionally includepressurizing the diaphragm to increase pressure in a vapor space of theimmersion tank. Increasing the pressure in the vapor space of theimmersion tank can cause a saturation temperature of the dielectricworking fluid to increase. The method can additionally include causingthe relief valve to release pressure from the diaphragm when thepressure in the vapor space of the immersion tank equals the diaphragmpressure.

In some embodiments, the method can include increasing a flow rate ofthe coolant to the subcooling heat exchanger in response to overclockingat least one component in at least one computing device of the pluralityof computing devices.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

Additional features and advantages will be set forth in the descriptionthat follows. Features and advantages of the disclosure may be realizedand obtained by means of the systems and methods that are particularlypointed out in the appended claims. Features of the present disclosurewill become more fully apparent from the following description andappended claims, or may be learned by the practice of the disclosedsubject matter as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otherfeatures of the disclosure can be obtained, a more particulardescription will be rendered by reference to specific embodimentsthereof which are illustrated in the appended drawings. For betterunderstanding, the like elements have been designated by like referencenumbers throughout the various accompanying figures. Understanding thatthe drawings depict some example embodiments, the embodiments will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 illustrates an example of an immersion cooling system inaccordance with at least one embodiment of the present disclosure.

FIG. 2 illustrates an example of a method for subcooling dielectricworking fluid in an immersion cooling system in accordance with at leastone embodiment of the present disclosure.

FIG. 3 illustrates another example of an immersion cooling system inaccordance with at least one embodiment of the present disclosure.

FIG. 4 illustrates an example of a method for using pressuremanipulation to increase the heat flux at the heat-generating componentsof computing devices in an immersion cooling system in accordance withat least one embodiment of the present disclosure.

FIG. 5A illustrates a perspective view of another example of animmersion cooling system in accordance with at least one embodiment ofthe present disclosure.

FIG. 5B is a perspective view of the immersion cooling system shown inFIG. 5A with a lid shown on top of the immersion tank.

DETAILED DESCRIPTION

The present disclosure is generally related to an improved immersioncooling system that can facilitate greater heat transfer away fromheat-generating components of computing devices (e.g., integratedcircuits such as CPUs) than is possible with currently availableimmersion cooling systems. More specifically, the techniques disclosedherein can enable greater heat flux at the heat-generating components ofcomputing devices than is possible with currently available immersioncooling systems.

An immersion cooling system in accordance with the present disclosurecan utilize subcooling to increase the heat flux at the heat-generatingcomponents of computing devices. The term “subcooling” refers to aliquid existing at a temperature below its normal boiling point.

When components of a computing device that is submerged in dielectricworking fluid generate heat and cause the dielectric working fluid toboil, this causes vapor bubbles to be generated at or near the surfaceof the heat-generating components. Subcooling the dielectric workingfluid can affect both the size of the vapor bubbles that are generatedand the frequency at which they are generated. More specifically,subcooling the dielectric working fluid can increase the frequency ofbubble generation. In addition, subcooling the dielectric working fluidcan reduce the diameter of the vapor bubbles that are generated. This isat least in part because the subcooled conditions cause bubblesdeparting from the surface of a heat-generating component to shrink asthey come in contact with cooler surrounding liquid. Both of theseeffects (increasing the frequency at which vapor bubbles are generated,and decreasing the diameter of the vapor bubbles that are generated) canincrease the maximum heat load the dielectric working fluid can carryaway from a heat-generating component.

Heat transfer through the boiling of a dielectric fluid, in the mannerdescribed above, is limited by a condition called the “critical heatflux.” In the context of immersion cooling, the critical heat flux canrefer to a point where the amount of heat that is generated by acomponent of a computing device becomes sufficiently large that thedeparture rate of bubbles (formed from boiling of the dielectric workingfluid) becomes insufficient to cool the component. Advantageously,subcooling can extend the critical heat flux of an immersion coolingsystem. In other words, subcooling can enable more heat to betransferred before the critical heat flux limitation occurs than wouldbe the case in the absence of subcooling.

One or more heat exchangers can be used to facilitate subcooling. Asnoted above, a two-phase immersion cooling system typically includes oneor more heat exchangers in the form of condensers that are positioned tocome into contact with vaporized working fluid, thereby causing thevaporized working fluid to condense back into a liquid and fall backinto the pool of dielectric working fluid. In accordance with thepresent disclosure, however, an immersion cooling system can alsoinclude one or more additional heat exchangers for the purpose offacilitating subcooling. The heat exchanger(s) that are used tofacilitate subcooling can be separate from the condensers that cause theworking fluid vapors to condense back into the pool of dielectric fluid.A heat exchanger that facilitates subcooling may be referred to hereinas a subcooling heat exchanger.

An immersion cooling system in accordance with the present disclosurecan include one or more subcooling heat exchangers that are positionedso that heat transfer can occur between the dielectric working fluid andthe subcooling heat exchanger(s). In some embodiments, one or moresubcooling heat exchangers can be submerged in the dielectric workingfluid. In some embodiments, one or more subcooling heat exchangers canbe embedded in an external wall of the immersion tank.

A subcooling heat exchanger can be in fluid communication with a sourceof coolant. The coolant source can provide coolant having a temperaturethat is lower than a boiling point of the dielectric working fluid. Theimmersion cooling system can also include a control system that controlshow much of the coolant flows into the subcooling heat exchanger basedat least in part on the temperature of the dielectric working fluid. Thecontrol system can include a temperature sensor that measures thetemperature of the dielectric working fluid, a valve that controls aflow of the coolant to the subcooling heat exchanger, and a controllerthat controls opening and closing of the valve based at least in part onthe temperature of the dielectric working fluid.

In some embodiments, the controller can be configured to calculate anerror value as a difference between a desired temperature of thedielectric working fluid and the temperature of the dielectric workingfluid as measured by the temperature sensor. The opening and the closingof the valve can be based at least in part on the error value. Forexample, if the desired temperature of the dielectric working fluid isgreater than or equal to the measured temperature, then the controllercan cause the valve to be closed in order to prevent coolant fromflowing to the subcooling heat exchanger. On the other hand, if themeasured temperature of the dielectric working fluid exceeds the desiredtemperature, then the controller can cause the valve to be opened sothat coolant can flow to the subcooling heat exchanger.

In some embodiments, an immersion cooling system in accordance with thepresent disclosure can also utilize the manipulation of pressure toincrease the heat flux at the heat-generating components of computingdevices. In other words, an immersion cooling system in accordance withthe present disclosure can utilize a combination of subcooling and themanipulation of pressure to achieve the benefits described herein. Aswith subcooling, the manipulation of pressure can also extend thecritical heat flux of an immersion cooling system.

Pressure manipulation can be accomplished through the use of adiaphragm. In some embodiments, the diaphragm can be located in thevapor space of the immersion tank. In this context, the vapor space ofthe immersion tank can refer to the part of the immersion tank that isdirectly above the pool of dielectric working fluid. When the dielectricworking fluid boils, vapors can rise into the vapor space of theimmersion tank.

The diaphragm can be separated from the rest of the immersion tank.Having the diaphragm in the immersion tank can cause the pressure in therest of the immersion tank to increase. This can cause the saturationtemperature of the dielectric working fluid to increase. Advantageously,increasing the saturation temperature of the dielectric working fluidcan increase the heat flux at the heat-generating components of thecomputing devices that are submerged in the dielectric working fluid.

A relief valve can be connected to the diaphragm. The relief valve canbe configured to release pressure from the diaphragm when the pressurein the vapor space of the immersion tank equals the pressure in thediaphragm.

As noted above, the techniques disclosed herein can enable greater heatflux at the heat-generating components of computing devices than ispossible with currently available immersion cooling systems. One of thebenefits of this additional heat flux is that it allows the computingdevices to be utilized to a greater extent than would otherwise bepossible. For example, the additional heat flux provided by thetechniques disclosed herein can enable the use of overclocking.

In general terms, overclocking is the practice of increasing the clockrate of a computer to exceed that certified by the manufacturer. Morespecifically, overclocking increases the operating speed of a givencomponent. Normally, overclocking is used to increase the performance ofa major chip or subsystem, such as the main processor or graphicscontroller. However, overclocking can also be used in connection withother components, such as system memory and/or system buses.

Overclocking causes an increase in power consumption. When a particularcomponent is overclocked, higher current and voltage are applied to thecomponent so that its power consumption increases. This can createthermal challenges.

Components of a computing device are typically designed for normaloperation, without overclocking. When a particular component isoverclocked, that component is pushed farther from a power perspective,thereby causing additional heat to be generated. An overclockedcomponent may be unreliable or fail completely if the additional heatload is not removed. The techniques disclosed herein, includingsubcooling and pressure manipulation, can be used to more effectivelyremove the additional heat that is produced by overclocking so thatoverclocking can be safely utilized.

There are many benefits that can be achieved through the use ofoverclocking. As just one example, consider a scenario where customersrent the use of virtual machines (VMs) that run on servers maintained bya cloud computing provider. By overclocking the processors in theservers, more VMs could be created. Alternatively, the same number ofVMs could be created, but the VMs could have improved performance.Alternatively still, some combination of more VMs and improvedperformance could be achieved. The techniques disclosed herein enablethese benefits to be realized by facilitating the use of overclocking ina safe, sustainable way.

FIG. 1 illustrates an example of an immersion cooling system 100 inaccordance with at least one embodiment of the present disclosure. Theimmersion cooling system 100 includes an immersion tank 102. Theimmersion tank 102 is configured to hold a plurality of computingdevices. For simplicity, FIG. 1 shows a single computing device in theimmersion tank 102. In particular, FIG. 1 shows a motherboard 104 in theimmersion tank 102. A plurality of heat-generating components arelocated on the motherboard 104. The heat-generating components caninclude integrated circuits 106 on the motherboard 104.

The immersion tank 102 is also configured to retain dielectric workingfluid 108. The computing devices are positioned in the immersion tank102 such that the computing devices are submerged in the dielectricworking fluid 108. FIG. 1 shows the motherboard 104 submerged in thedielectric working fluid 108.

As discussed above, the computing devices in the immersion tank 102generate heat during normal operation. The dielectric working fluid 108has a relatively low boiling point such that heat absorbed by thedielectric working fluid 108 surrounding the computing devices causes aportion of the dielectric working fluid 108 to boil off or vaporize intoa gas. The vapors produced by the boiling of the dielectric workingfluid 108 rise above the fluid pool into a part of the immersion tank102 that may be referred to herein as a vapor space 110. The vapor space110 is located above the dielectric working fluid 108. FIG. 1 showsvaporized working fluid 112 rising up above the pool of dielectricworking fluid 108. As the vaporized working fluid 112 continues to rise,it will enter the vapor space 110 of the immersion tank 102.

The immersion cooling system 100 includes a condenser 114 located in thevapor space 110 of the immersion tank 102. The condenser 114 is in fluidcommunication with a coolant source 116. The coolant source 116 can beany system that is capable of supplying coolant to the immersion coolingsystem 100.

In some embodiments, the coolant can be any fluid that has a higherthermal transfer rate than the dielectric working fluid 108, and is aliquid at and below the boiling point of the dielectric working fluid108. One example of a coolant that could be used is water. However, thisexample should not be interpreted as limiting the scope of the presentdisclosure. There are many other fluids that could be used as thecoolant.

When the coolant source 116 supplies the coolant to the immersioncooling system 100, the temperature of the coolant is lower than theboiling point of the dielectric working fluid 108. Therefore, as thecoolant flows through the condenser 114, the condenser 114 is cooled.The condenser 114 is positioned so that it will cause condensation ofvaporized working fluid 112. In the depicted embodiment, the condenser114 is positioned directly above the dielectric working fluid 108, sothat it will come into direct contact with vaporized working fluid 112.Therefore, when coolant flows through the condenser 114, the condenser114 will cause the vaporized working fluid 112 to condense back into aliquid and fall back into the pool of dielectric working fluid 108.

A pump (not shown) causes the coolant to flow through the condenser 114.For purposes of the present discussion, it will be assumed that thecoolant flows from left to right in FIG. 1 . Coolant enters an inlet 118of the condenser 114. As vaporized working fluid 112 comes into contactwith the condenser 114, the coolant is heated. Heated coolant exits outof an outlet 120 of the condenser 114. FIG. 1 shows the heated coolantbeing returned to a coolant return 122. The coolant return 122 can beany device or system that is capable of receiving heated coolant fromthe immersion cooling system 100.

The arrows from the coolant source 116 to the inlet 118 of the condenser114 represent one or more pipes that deliver the coolant from thecoolant source 116 to the inlet 118 of the condenser 114. Similarly, thearrows from the outlet 120 of the condenser 114 to the coolant return122 represent one or more pipes that deliver the heated coolant from theoutlet 120 of the condenser 114 to the coolant return 122.

In addition to the condenser 114, the immersion cooling system 100 alsoincludes another heat exchanger. This other heat exchanger may bereferred to herein as a subcooling heat exchanger 124. Whereas thecondenser 114 causes condensation of vaporized working fluid 112, thesubcooling heat exchanger 124 is positioned so that it will facilitatesubcooling of the dielectric working fluid 108. In other words, thesubcooling heat exchanger 124 is positioned so that it will cause heattransfer to occur between the dielectric working fluid 108 and thesubcooling heat exchanger 124. In the depicted embodiment, thesubcooling heat exchanger 124 is submerged in the dielectric workingfluid 108, so that the subcooling heat exchanger 124 will come intodirect contact with the dielectric working fluid 108.

Like the condenser 114, the subcooling heat exchanger 124 is also influid communication with the coolant source 116. A pump (not shown)causes the coolant to enter an inlet 126 of the subcooling heatexchanger 124 and flow through the subcooling heat exchanger 124. As thecoolant flows through the subcooling heat exchanger 124, the subcoolingheat exchanger 124 will subcool the dielectric working fluid 108. Asdiscussed above, subcooling the dielectric working fluid 108 canincrease the frequency of bubble generation while also reducing thediameter of the vapor bubbles that are generated. Both of these effectscan increase the maximum heat load the dielectric working fluid 108 cancarry away from the heat-generating components (e.g., the integratedcircuits 106) on the motherboard 104. As the coolant flows through thesubcooling heat exchanger 124 and it subcools the dielectric workingfluid 108, the coolant is heated. Heated coolant exits out of an outlet128 of the subcooling heat exchanger 124. FIG. 1 shows the heatedcoolant being returned to the coolant return 122.

In the depicted embodiment, the same coolant source 116 is shownproviding coolant to the condenser 114 and also to the subcooling heatexchanger 124. In alternative embodiments, however, different coolantsources could be used. For example, a first coolant source could providecoolant to the condenser 114, and a second coolant source that isdifferent from the first coolant source could provide coolant to thesubcooling heat exchanger 124.

Similarly, in the depicted embodiment, the same coolant return 122 isshown receiving coolant from the condenser 114 and from the subcoolingheat exchanger 124. In alternative embodiments, however, differentcoolant returns could be used. For example, a first coolant return couldreceive coolant from the condenser 114, and a second coolant return thatis different from the first coolant return could receive coolant fromthe subcooling heat exchanger 124.

The immersion cooling system 100 includes a control system 130 thatcontrols the extent to which the dielectric working fluid 108 issubcooled. More specifically, the control system 130 is configured tocontrol how much of the coolant flows into the subcooling heat exchanger124 based at least in part on the temperature of the dielectric workingfluid 108. The control system 130 includes a valve 132, a controller134, and a temperature sensor 136. The valve 132 controls the flow ofcoolant to the subcooling heat exchanger 124. The controller 134controls the opening and the closing of the valve 132 based at least inpart on the temperature of the dielectric working fluid 108. In FIG. 1 ,the controller 134 is shown connected to a power supply 150. Thetemperature sensor 136 measures the temperature of the dielectricworking fluid 108.

When the valve 132 is open, coolant can flow to the subcooling heatexchanger 124. Conversely, when the valve 132 is closed, coolant isprevented from flowing to the subcooling heat exchanger 124. In someembodiments, the valve 132 can be capable of one or more intermediatestates between fully opened and fully closed. For example, the valve 132can be capable of being partially opened. When the valve 132 ispartially opened, the rate of coolant flow can be greater than zero butless than when the valve 132 is fully opened.

In some embodiments, the controller 134 can be configured tocontinuously calculate an error value. The error value can be calculatedas the difference between (a) the desired temperature of the dielectricworking fluid 108, and (b) the actual temperature of the dielectricworking fluid 108 (e.g., as measured by the temperature sensor 136). Tofacilitate subcooling, the desired temperature of the dielectric workingfluid 108 can be set to be below the boiling point of the dielectricworking fluid 108.

The controller 134 can then open or close the valve 132 depending on theerror value that is calculated. For example, if (a) is greater than orequal to (b), then the controller 134 can close the valve 132. On theother hand, if (b) exceeds (a), then the controller 134 can open thevalve 132 and allow coolant to flow to the subcooling heat exchanger124. In some embodiments, the extent to which the valve 132 is openedcan depend at least in part on the extent to which (b) exceeds (a). Forexample, if (b) greatly exceeds (a), then the valve 132 can be opened toa greater extent than if (b) only slightly exceeds (a).

In some embodiments, the controller 134 can be implemented as aproportional-integral-derivative (PID) controller. A PID controllercontinuously calculates an error value (such as the error valuedescribed above) and applies a correction based on proportional,integral, and derivative terms.

In the depicted embodiment, the valve 132 controls the supply of coolantto the subcooling heat exchanger 124, but does not control the supply ofcoolant to the condenser 114. In some alternative embodiments, a valvecould be provided that controls the supply of coolant to both thesubcooling heat exchanger 124 and also to the condenser 114. In someother alternative embodiments, at least two different valves could beprovided. A first valve could control the supply of coolant to thesubcooling heat exchanger 124, and a second valve that is different fromthe first valve could control the supply of coolant to the condenser114.

In some embodiments, the control system 130 can be configured to useinformation about the expected or incoming workload of the computingdevices in the immersion tank 102 for the purpose of controlling theflow of coolant to the subcooling heat exchanger 124. In other words,information about the expected or incoming workload can be usedproactively to control the flow of coolant to the subcooling heatexchanger 124.

As noted above, the immersion cooling system 100 can be used in adatacenter. The datacenter can include a plurality of immersion tankslike the immersion tank 102 shown in FIG. 1 . A workload allocator 160can be responsible for allocating workloads among the computing devicesin the various immersion tanks. For example, the workload allocator 160can be responsible for allocating virtual machines (VMs) among thecomputing devices in the various immersion tanks. The control system 130can be in electronic communication with the workload allocator 160. Theworkload allocator 160 can include a predictive element 162 thatprovides for proactive subcooling. The workload allocator 160 canprovide information and/or signals to the control system 130 that causethe flow of coolant to the subcooling heat exchanger 124 to be adjustedbased on the expected or predicted workload to be experienced by thecomputing devices in the immersion tank 102.

In one possible scenario, the predictive element 162 of the workloadallocator 160 could predict that the computing devices in the immersiontank 102 will have increased workload (e.g., that additional VMs will beallocated) at a certain time of day. Based at least in part on thisprediction, the workload allocator 160 can provide information and/orsignals to the control system 130 that cause the flow of coolant to thesubcooling heat exchanger 124 to be increased during this time of day.

The opposite scenario could also occur. The predictive element 162 ofthe workload allocator 160 could predict that the computing devices inthe immersion tank 102 will have decreased workload (e.g., that fewerVMs will be allocated) at a certain time of day. Based at least in parton this prediction, the workload allocator 160 can provide informationand/or signals to the control system 130 that cause the flow of coolantto the subcooling heat exchanger 124 to be decreased during this time ofday.

Predictions made by the predictive element 162 of the workload allocator160 can be based at least in part on historical data about the workloadexperienced by the computing devices in the immersion tank 102 (and inother immersion tanks in the immersion cooling system 100). In someembodiments, machine learning techniques can be utilized to make suchpredictions.

As discussed above, the additional heat flux provided by the techniquesdisclosed herein can enable the use of overclocking. In someembodiments, the predictive element 162 of the workload allocator 160can predict when overclocking will be utilized. When a prediction ismade that overclocking will be utilized during a particular period oftime, the workload allocator 160 can provide information and/or signalsto the control system 130 that cause the flow of coolant to thesubcooling heat exchanger 124 to be increased to compensate for theadditional power consumption caused by overclocking.

The immersion cooling system 100 shown in FIG. 1 includes just onesubcooling heat exchanger 124 submerged in the dielectric working fluid108. In some alternative embodiments, an immersion cooling system 100could include a plurality of subcooling heat exchangers submerged indielectric working fluid 108. In some embodiments, the plurality ofsubcooling heat exchangers could be in fluid communication with the samecoolant source and the same coolant return. In other embodiments, theplurality of subcooling heat exchangers could be in fluid communicationwith different coolant sources and/or with different coolant returns.

The immersion cooling system 100 also includes a pump 138 thatcirculates the dielectric working fluid 108 throughout the immersiontank 102. Circulating the dielectric working fluid 108 throughout theimmersion tank 102 helps to ensure that the temperature of thedielectric working fluid 108 is substantially uniform.

In addition to circulating the dielectric working fluid 108 throughoutthe immersion tank 102, the pump 138 also causes the dielectric workingfluid 108 to flow through a pipe 140 that is positioned near thecomputing devices that are being cooled. In FIG. 1 , where only a singlecomputing device (i.e., the motherboard 104) is shown, the pipe 140 ispositioned close to that computing device. The pipe 140 includes aplurality of nozzles 142. When the pump 138 causes the dielectricworking fluid 108 to flow through the pipe 140, this causes streams ofdielectric working fluid 108 to exit out of the nozzles 142 in thedirection of the heat-generating components (e.g., the integratedcircuits 106) on the motherboard 104. In addition to helping to ensurethat the temperature of the dielectric working fluid 108 issubstantially uniform, aiming streams of dielectric working fluid 108 atthe heat-generating components on the motherboard 104 also helps to coolthe heat-generating components.

The embodiment shown in FIG. 1 includes just a single pump 138 and asingle pipe 140 with nozzles 142. However, an immersion cooling system100 in accordance with the present disclosure could include a pluralityof pumps and/or a plurality of pipes with nozzles. The pumps and/or thepipes with nozzles could be placed in a variety of different locationsthroughout the immersion tank 102.

In FIG. 1 , the pipe 140 with the nozzles 142 is located beneath thebottom side of the motherboard 104. In an alternative embodiment, a pipewith nozzles could be located near the left side, the right side, and/orthe top side of the motherboard 104. If the immersion tank 102 includesa plurality of computing devices, pipes with nozzles can be located insimilar positions with respect to the plurality of computing devices.

In FIG. 1 , the pump 138 is located near an inlet 144 to the pipe 140with the nozzles 142. In embodiments that include a plurality of pipessimilar to the pipe 140 shown in FIG. 1 , a plurality of pumps could beprovided. The pumps could be positioned such that at least one pump islocated near at least one inlet to each pipe in the immersion tank 102.

The immersion cooling system 100 includes a temperature sensor 146 thatis configured to measure the temperature of the vapor space 110 of theimmersion tank 102. The immersion cooling system 100 also includes apressure sensor 148 that is configured to measure the pressure of thevapor space 110 of the immersion tank 102. The temperature sensor 146and the pressure sensor 148 can be used to control the rate of coolantflow through the condenser 114. More specifically, based on thetemperature that is measured, the temperature sensor 146 can send asignal to a controller (not shown) that controls the rate of coolantflow through the condenser. Similarly, based on the pressure that ismeasured, the pressure sensor 148 can also send a signal to thecontroller. The controller can control the rate of coolant flow throughthe condenser 114 based at least in part on the signals received fromthe temperature sensor 146 and the pressure sensor 148.

FIG. 2 illustrates an example of a method 200 for subcooling dielectricworking fluid in an immersion cooling system in accordance with at leastone embodiment of the present disclosure. For the sake of clarity, themethod 200 will be described in relation to the immersion cooling system100 shown in FIG. 1 . The method 200 can be implemented by a controlsystem, such as the control system 130 in the immersion cooling system100 of FIG. 1 .

The method 200 can include determining 201 the desired temperature ofthe dielectric working fluid 108 (T_(desired)). In some embodiments,T_(desired) can be set to be a pre-determined amount below thesaturation temperature (T_(sat)) of the dielectric working fluid 108.For example, T_(desired) can be set to be N degrees below T_(sat), whereN can be a configurable parameter. In some embodiments, N can be atleast 10° C. In other words, in some embodiments T_(desired) can be setto be at least 10° C. below T_(sat).

The value of T_(sat) varies based on the type of dielectric workingfluid 108 that is being used. As an example, a typical range for T_(sat)is from about 34° C. to about 60° C.

The method 200 can also include determining 203 the measured temperatureof the dielectric working fluid 108 (T_(measured)). In some embodiments,determining T_(measured) can include receiving one or more temperaturemeasurements from one or more temperature sensors, such as thetemperature sensor 136 shown in FIG. 1 .

The method 200 can also include calculating 205 an error value as thedifference between T_(desired) and T_(measured). One skilled in the artwill understand that calculating the difference between T_(desired) andT_(measured) can be achieved by performing the calculationT_(desired)—T_(measured) or by performing the calculation T_(measured)T_(desired).

The method 200 can also include determining 207 how to adjust the flowof coolant to the subcooling heat exchanger 124 based at least in parton the error value that is calculated. For example, when T_(measured) isgreater than T_(desired), the method 200 can include causing 209 thecoolant to flow to the subcooling heat exchanger 124 based at least inpart on the error value that is calculated. On the other hand, whenT_(desired) is greater than or equal to T_(measured), the method 200 caninclude preventing 211 the flow of coolant to the subcooling heatexchanger 124.

When T_(measured) is greater than T_(desired) and the method 200includes causing 209 the coolant to flow to the subcooling heatexchanger 124 based at least in part on the error value that iscalculated, there are several different ways that the rate of coolantflow can be determined. In some embodiments, the flow of coolant to thesubcooling heat exchanger 124 can depend at least in part on themagnitude of the difference between T_(measured) and T_(desired). Forexample, the controller 134 can cause more coolant to flow to thesubcooling heat exchanger 124 (or, in other words, cause coolant to flowto the subcooling heat exchanger 124 at a faster rate) when T_(measured)is significantly greater than T_(desired) as compared to whenT_(measured) is only slightly greater than T_(desired).

In some embodiments, the flow of coolant to the subcooling heatexchanger 124 can be directly proportional to the difference betweenT_(measured) and T_(desired). For example, consider a scenario in whichT_(measured)−T_(desired)=2n at time t₁, and T_(measured) T_(desired)=nat time t₂. In this scenario, the rate of coolant flow to the subcoolingheat exchanger 124 could be twice as great at time t₁ as it is at timet₂.

In some embodiments, causing 209 the coolant to flow to the subcoolingheat exchanger 124 can include causing a valve 132 that controls theflow of the coolant to the subcooling heat exchanger 124 to be opened.The extent to which the valve 132 is opened can depend on the desiredrate of coolant flow. For example, the valve 132 can be opened to agreater extent when a higher rate of coolant flow is desired as comparedto when a lesser rate of coolant flow is desired.

As discussed above, the additional heat flux provided by the techniquesdisclosed herein can enable the use of overclocking. When one or morecomputing devices in an immersion tank are overclocked, this can causean increase in power consumption. The increase in power consumption cancause the temperature of the dielectric working fluid to increase. Forexample, reference is once again made to the immersion cooling system100 shown in FIG. 1 and the method 200 shown in FIG. 2 . If one or morecomponents (e.g., a CPU) on the motherboard 104 is overclocked, theresulting increase in power consumption can cause the temperature of thedielectric working fluid 108 in the immersion tank 102 to increase. Theincrease in power consumption can cause the error value (i.e., thedifference between T_(desired) and T_(measured) that is calculated 205in the method 200 shown in FIG. 2 ) to increase. The increase in theerror value can therefore cause 209 the coolant to flow to thesubcooling heat exchanger 124 at a higher rate.

FIG. 3 illustrates another example of an immersion cooling system 300 inaccordance with at least one embodiment of the present disclosure. Theimmersion cooling system 300 is similar in several respects to theimmersion cooling system 100 shown in FIG. 1 . For example, theimmersion cooling system 300 includes an immersion tank 302 that isconfigured to hold a plurality of computing devices. For the sake ofsimplicity, FIG. 3 shows a single computing device in the immersion tank302, namely a motherboard 304. A plurality of heat-generating components(e.g., integrated circuits 306) are located on the motherboard 304. Theimmersion tank 302 is also configured to retain dielectric working fluid308 such that the computing devices in the immersion tank 302 aresubmerged in the dielectric working fluid 308. FIG. 3 shows themotherboard 304 submerged in the dielectric working fluid 308.

The immersion cooling system 300 also includes a pump 338. In additionto circulating the dielectric working fluid 308 throughout the immersiontank 302, the pump 338 also causes the dielectric working fluid 308 toflow through a pipe 340 that is positioned near the computing devicesthat are being cooled. The pipe 340 includes a plurality of nozzles 342.When the pump 338 causes the dielectric working fluid 308 to flowthrough the pipe 340, this causes streams of dielectric working fluid308 to exit out of the nozzles 342 in the direction of theheat-generating components (e.g., the integrated circuits 306) on themotherboard 304.

The immersion cooling system 300 is shown with a temperature sensor 336that is configured to measure the temperature of the dielectric workingfluid 308. The immersion cooling system 300 is also shown with atemperature sensor 346 that is configured to measure the temperature ofthe vapor space 310 of the immersion tank 302.

The immersion cooling system 300 is also different in many respects fromthe immersion cooling system 100 shown in FIG. 1 . For example, asdiscussed above, the immersion cooling system 100 of FIG. 1 includes acondenser 114 in the vapor space 110 of the immersion tank 102 and asubcooling heat exchanger 124 submerged in the dielectric working fluid108. In contrast, the immersion cooling system 300 shown in FIG. 3 doesnot include any heat exchangers within the internal part of theimmersion tank 302. Instead, the immersion cooling system 300 includes aplurality of condensers and a plurality of subcooling heat exchangersembedded in the external walls of the immersion tank 302.

More specifically, a first external wall 352-1 of the immersion tank 302includes a plurality of channels that carry coolant from a coolantsource 316. A first plurality of upper channels 314-1 are positioned inan upper half of the immersion tank 302, near the vapor space 310 of theimmersion tank 302. Because the first plurality of upper channels 314-1are positioned near the vapor space 310 of the immersion tank 302, thefirst plurality of upper channels 314-1 act as condensers. Thus, thefirst plurality of upper channels 314-1 cause condensation of vaporizedworking fluid 312. A first plurality of lower channels 324-1 arepositioned in a lower half of the immersion tank 302, near the computingdevices submerged in the dielectric working fluid 308. Because the firstplurality of lower channels 324-1 are positioned near the computingdevices submerged in the dielectric working fluid 308, the firstplurality of lower channels 324-1 act as subcooling heat exchangers.Thus, the first plurality of lower channels 324-1 facilitate subcoolingof the dielectric working fluid 308.

Similarly, a second external wall 352-2 of the immersion tank 302includes a plurality of channels that carry heated coolant to a coolantreturn 322. A second plurality of upper channels 314-2 are positioned inan upper half of the immersion tank 302, near the vapor space 310 of theimmersion tank 302. A second plurality of lower channels 324-2 arepositioned in a lower half of the immersion tank 302, near the computingdevices submerged in the dielectric working fluid 308.

Having the condensers (i.e., the first plurality of upper channels 314-1and the second plurality of upper channels 314-2) and the subcoolingheat exchangers (i.e., the first plurality of lower channels 324-1 andthe second plurality of lower channels 324-2) outside of the immersiontank 302 creates additional space inside the immersion tank 302. Thisadditional space can be utilized for pressure manipulation techniquesthat facilitate greater heat transfer away from heat-generatingcomponents of computing devices.

In the depicted embodiment, a diaphragm 354 can be included in the vaporspace 310 of the immersion tank 302. The diaphragm 354 can be formed inthe lid 356 of the immersion tank 302. A partition 358 can extenddownward from the lid 356 and separate the diaphragm 354 from the restof the immersion tank 302.

Because the diaphragm 354 is separated from the rest of the immersiontank 302, the pressure inside the diaphragm 354 can be different fromthe pressure in the rest of the immersion tank 302. In the discussionthat follows, the pressure inside the diaphragm 354 may be referred toas P_(dia). The pressure in the vapor space 310 of the immersion tank302 may be referred to as P_(in/vap).

The diaphragm 345 can be used to manipulate P_(in/vap). In somesituations, having the diaphragm 354 in the immersion tank 302 can causeP_(in/vap) to increase. In other words, P_(in/vap) can be higher withthe diaphragm 354 in the immersion tank 302 than it would otherwise bewithout the diaphragm 354. Moreover, increasing P_(in/vap) can cause thesaturation temperature of the dielectric working fluid 308 (T_(sat)) toincrease. In this context, T_(sat) is the temperature for acorresponding saturation pressure (P_(sat)) at which the dielectricworking fluid 308 boils into its vapor phase. Advantageously, increasingT_(sat) of the dielectric working fluid 308 can increase the heat fluxat the heat-generating components of the computing devices that aresubmerged in the dielectric working fluid 308.

In other situations, having the diaphragm 354 in the immersion tank 302can cause P_(in/vap) to decrease. In other words, P_(in/vap) can belower with the diaphragm 354 in the immersion tank 302 than it wouldotherwise be without the diaphragm 354. Moreover, decreasing P_(in/vap)can cause the saturation temperature of the dielectric working fluid 308(T_(sat)) to decrease.

Therefore, the presence of the diaphragm 354 in the immersion tank 302can cause P_(in/vap) to increase or decrease, which can cause T_(sat) ofthe dielectric working fluid 308 to increase or decrease. Using thediaphragm 345 to manipulate P_(in/vap) in this way can have the effectof increasing the amount of heat that can be transferred by theimmersion cooling system 300.

A relief valve 360 can be connected to the diaphragm 354. The reliefvalve 360 can be configured to release pressure from the diaphragm 354when P_(dia) equals P_(in/vap). More specifically, whenP_(in/vap)<P_(dia), pressure can continue to accumulate in the vaporspace 310 of the immersion tank 302 such that P_(sat) of the dielectricworking fluid 308 increases. When P_(in/vap) becomes equal to P_(dia),the relief valve 360 can release pressure from the diaphragm 354.

The immersion cooling system 300 includes a pressure sensor 362 that isconfigured to measure P_(dia.) and a pressure sensor 348 that isconfigured to measure P_(in/vap).

In the depicted embodiment, the diaphragm 354 is shown in the immersiontank 302. However, in an alternative embodiment, the diaphragm could belocated outside of the immersion tank. As long as one side of thediaphragm is connected to the headspace of the immersion tank (eitherdirectly or through a connecting orifice), the pressure of the headspacecan be regulated without directly injecting additional material into theimmersion tank. In some embodiments, a diaphragm that is located outsidethe immersion tank could be constructed through the use of a hydraulicsystem that includes an accumulator. In such embodiments, the pressureon the opposing side of the diaphragm could be regulated to changerelative pressure and thus influence headspace pressure.

FIG. 4 illustrates an example of a method 400 for using pressuremanipulation to increase the heat flux at the heat-generating componentsof computing devices in an immersion cooling system in accordance withat least one embodiment of the present disclosure. For the sake ofclarity, the method 400 will be described in relation to the immersioncooling system 300 shown in FIG. 3 .

The method 400 can include pressurizing 401 the diaphragm 354. Thediaphragm 354 can be pressurized 401 to a point where the presence ofthe diaphragm 354 in the immersion tank 302 causes P_(in/vap) to behigher than it otherwise would be without the diaphragm 354. Asdiscussed above, causing P_(in/vap) to increase can cause T_(sat) of thedielectric working fluid 308 to increase, which can thereby increase theamount of heat that can be transferred by the immersion cooling system300.

The method 400 can also include monitoring 403 the pressure inside thediaphragm 354 (P_(dia)) and the pressure in the vapor space 310 of theimmersion tank 302 (P_(in/vap)). In some embodiments, monitoring 403P_(dia) and P_(in/vap) can include receiving one or more pressuremeasurements from one or more pressure sensors.

The method 400 can also include comparing P_(dia) and P_(in/vap) todetermine 405 whether P_(dia) equals P_(in/vap). As long asP_(in/vap)<P_(dia), pressure can continue to accumulate in the vaporspace 310 of the immersion tank 302. However, when it is determined 405that P_(in/vap) is equal to P_(dia), the method 400 can include causing407 the relief valve 360 to release pressure from the diaphragm 354.

FIG. 5A illustrates a perspective view of another example of animmersion cooling system 500 in accordance with at least one embodimentof the present disclosure. The immersion cooling system 500 representsone possible implementation of the immersion cooling system 300 shown inFIG. 3 .

The immersion cooling system 500 includes an immersion tank 502 that isconfigured to hold a plurality of computing devices 504. The immersiontank 502 is configured to retain dielectric working fluid (not shown inFIGS. 5A-B) such that the computing devices in the immersion tank 502are submerged in the dielectric working fluid.

A first external wall 552-1 of the immersion tank 502 includes aplurality of channels that carry coolant from a coolant source (notshown in FIGS. 5A-B). A first plurality of upper channels 514-1 arepositioned in an upper half of the immersion tank 502, near the vaporspace of the immersion tank 502. The first plurality of upper channels514-1 act as condensers that cause condensation of vaporized workingfluid. A first plurality of lower channels 524-1 are positioned in alower half of the immersion tank 502, near the computing devices 504submerged in the dielectric working fluid. The first plurality of lowerchannels 524-1 act as subcooling heat exchangers that facilitatesubcooling of the dielectric working fluid.

Similarly, a second external wall 552-2 of the immersion tank 502includes a plurality of channels that carry heated coolant to a coolantreturn (not shown in FIGS. 5A-B). A second plurality of upper channels514-2 are positioned in an upper half of the immersion tank 502, nearthe vapor space of the immersion tank 502. A second plurality of lowerchannels 524-2 are positioned in a lower half of the immersion tank 502,near the computing devices 504 submerged in the dielectric workingfluid.

A pump (not shown) can cause the coolant to flow into the firstplurality of upper channels 514-1 and the first plurality of lowerchannels 524-1. The coolant in the first plurality of upper channels514-1 causes the vaporized working fluid to condense, and the coolant inthe first plurality of lower channels 524-1 subcools the dielectricworking fluid. This causes the coolant to become heated. The secondplurality of upper channels 514-2 and the second plurality of lowerchannels 524-2 carries heated coolant to a coolant return.

FIG. 5B is a perspective view of the immersion cooling system 500 shownin FIG. 5A with a lid 556 shown on top of the immersion tank 502. Insome embodiments, a diaphragm (not shown in FIGS. 5A-B) can be formed inthe lid 556. The diaphragm can be similar to the diaphragm 354 shown inFIG. 3 . As discussed above, the diaphragm can be used for pressuremanipulation techniques that increase the heat flux at theheat-generating components of the computing devices 504 that aresubmerged in the dielectric working fluid.

Some examples of various terms and phrases that have been used in theabove discussion will now be provided.

The term “heat flux” refers to the rate of thermal energy flow per unitsurface area of a heat transfer surface.

The term “immersion tank” may refer to any container that issufficiently large and sturdy to retain a plurality of computing devicesthat are submerged in dielectric working fluid.

The term “dielectric working fluid” (or simply “working fluid”) mayrefer to any nonconductive fluid in which computing devices can besubmerged for the purpose of cooling the computing devices. Someexamples of dielectric working fluids that can be used include syntheticfluids, fluorocarbon-based fluids, mineral oil, and deionized water. Adielectric working fluid may have a relatively low boiling point (e.g.,40-50° C.), such that heat generated by computing devices would normallycause the dielectric working fluid to boil.

The term “condenser” may refer to any apparatus that may be used tocondense vaporized working fluid. In some embodiments, a condenser mayinclude one or more tubes, which may be shaped in the form of one ormore coils. Cool liquid may be pumped through the tubes to facilitatecondensation of vaporized working fluid.

In some embodiments, two structures are in “fluid communication” withone another if there is a path for a fluid to flow between the twostructures. In this context, the term “fluid” may refer generally to anysubstance that has the tendency to assume the shape of its container,and may include a liquid or a gas.

The term “controller” may refer to hardware, software, firmware, or anycombination thereof, that performs some or all of the steps, operations,actions, or other functionality disclosed herein in connection with thecontroller. If implemented in software, the techniques may be realizedat least in part by a non-transitory computer-readable medium havingcomputer-executable instructions stored thereon that, when executed byat least one processor, implement the disclosed functionality.

As noted above, the “vapor space” of the immersion tank can refer to thepart of the immersion tank that is directly above the pool of dielectricworking fluid. In some contexts, the term “headspace” can be synonymouswith the term “vapor space.” In other contexts, the term “headspace” canrefer to a part of the immersion tank that is distinct from the vaporspace. For example, the term “headspace” can refer to a part of theimmersion tank that is above the vapor space.

The steps, operations, and/or actions of the methods described hereinmay be interchanged with one another without departing from the scope ofthe claims. In other words, unless a specific order of steps,operations, and/or actions is required for proper functioning of themethod that is being described, the order and/or use of specific steps,operations, and/or actions may be modified without departing from thescope of the claims.

The term “determining” (and grammatical variants thereof) can encompassa wide variety of actions. For example, “determining” can includecalculating, computing, processing, deriving, investigating, looking up(e.g., looking up in a table, a database or another data structure),ascertaining and the like. Also, “determining” can include receiving(e.g., receiving information), accessing (e.g., accessing data in amemory) and the like. Also, “determining” can include resolving,selecting, choosing, establishing and the like.

The terms “comprising,” “including,” and “having” are intended to beinclusive and mean that there can be additional elements other than thelisted elements. Additionally, it should be understood that referencesto “one embodiment” or “an embodiment” of the present disclosure are notintended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. For example, anyelement or feature described in relation to an embodiment herein may becombinable with any element or feature of any other embodiment describedherein, where compatible.

The present disclosure may be embodied in other specific forms withoutdeparting from its spirit or characteristics. The described embodimentsare to be considered as illustrative and not restrictive. The scope ofthe disclosure is, therefore, indicated by the appended claims ratherthan by the foregoing description. Changes that come within the meaningand range of equivalency of the claims are to be embraced within theirscope.

What is claimed is:
 1. A method for subcooling a dielectric workingfluid in an immersion cooling system that comprises a plurality ofcomputing devices, the method comprising: determining a desiredtemperature of the dielectric working fluid, wherein the desiredtemperature of the dielectric working fluid is less than a boiling pointof the dielectric working fluid; calculating an error value as adifference between the desired temperature of the dielectric workingfluid and a measured temperature of the dielectric working fluid;causing coolant to flow to a subcooling heat exchanger based at least inpart on the error value when the measured temperature of the dielectricworking fluid is greater than the desired temperature of the dielectricworking fluid; and preventing the coolant from flowing to the subcoolingheat exchanger when the measured temperature of the dielectric workingfluid is less than or equal to the desired temperature of the dielectricworking fluid.
 2. The method of claim 1, further comprising increasing aflow rate of the coolant to the subcooling heat exchanger in response tooverclocking at least one component in at least one computing device ofthe plurality of computing devices.
 3. The method of claim 1, furthercomprising adjusting a flow rate of the coolant to the subcooling heatexchanger in response to an expected workload of the plurality ofcomputing devices.
 4. The method of claim 1, wherein the subcooling heatexchanger is submerged in the dielectric working fluid.
 5. The method ofclaim 1, wherein the subcooling heat exchanger is embedded in anexternal wall of an immersion tank of the immersion cooling system.
 6. Amethod of transferring heat from a heat-generating component at leastpartially submerged in a dielectric working fluid in an immersioncooling system, the method comprising: pressurizing a diaphragm, whereinthe heat-generating component and the dielectric working fluid arepositioned in an immersion tank of the immersion cooling system, andwherein the diaphragm is positioned in a vapor space of the immersiontank; increasing a vapor space pressure of the vapor space; based onincreasing the vapor space pressure, causing an increase in a saturationtemperature of the dielectric working fluid; and causing an increase ina heat flux from the heat-generating component to the dielectric workingfluid based on increasing the saturation temperature.
 7. The method ofclaim 6, wherein increasing the heat flux by pressurizing the diaphragmis in response to overclocking the heat-generating component.
 8. Themethod of claim 7, further comprising monitoring a diaphragm pressure ofthe diaphragm and monitoring the tank pressure.
 9. The method of claim8, further comprising continuing to pressurize the diaphragm based ondetermining that the diaphragm pressure is greater than the tankpressure.
 10. The method of claim 8, further comprising releasingpressure from the diaphragm based on determining that the tank pressureis equal to the diaphragm pressure.
 11. The method of claim 10, whereinreleasing pressure from the diaphragm includes opening a pressure reliefvalve of the diaphragm.
 12. The method of claim 6, wherein the immersioncooling system is a two-phase immersion cooling system.
 13. An immersioncooling system, comprising: an immersion tank that is configured toretain a dielectric working fluid and to hold a plurality of computingdevices submerged in the dielectric working fluid; a condenser that isconfigured to cause condensation of vaporized working fluid; and adiaphragm that changes a vapor space pressure in a vapor space of theimmersion tank, wherein changing the vapor space pressure also changes asaturation temperature of the dielectric working fluid.
 14. Theimmersion cooling system of claim 13, further comprising a subcoolingheat exchanger that is in fluid communication with a coolant source, thecoolant source providing coolant having a coolant temperature that islower than a boiling point of the dielectric working fluid, thesubcooling heat exchanger being positioned so that heat transfer canoccur between the dielectric working fluid and the subcooling heatexchanger.
 15. The immersion cooling system of claim 14, furthercomprising a means for controlling how much of a flow of the coolantflows into the subcooling heat exchanger, wherein the flow of thecoolant into the subcooling heat exchanger is based at least in part ona temperature of the dielectric working fluid.
 16. The immersion coolingsystem of claim 14, wherein: the condenser is located in a vapor spaceof the immersion tank; and the subcooling heat exchanger is submerged inthe dielectric working fluid.
 17. The immersion cooling system of claim14, wherein: the diaphragm is located in the vapor space of theimmersion tank; and the condenser and the subcooling heat exchanger areembedded in an external wall of the immersion tank.
 18. The immersioncooling system of claim 13, further comprising a relief valve forreleasing a pressure of the diaphragm.
 19. The immersion cooling systemof claim 18, wherein the relief valve is configured to release thepressure of the diaphragm when the vapor space pressure equals adiaphragm pressure.
 20. The immersion cooling system of claim 13,wherein: the immersion cooling system further comprises a pipe that issubmerged in the dielectric working fluid, the pipe comprising aplurality of nozzles and a pump that forces the dielectric working fluidto flow through the pipe; and the pipe is positioned to cause aplurality of streams of the dielectric working fluid to exit out of theplurality of nozzles in a direction of at least one heat-generatingcomponent on at least one computing device.